The present invention relates generally to means for welding together a pair of moldable plastic units. More particularly, the invention relates to a device for welding moldable plastic branch pipes upon a plastic main pipe. The invention involves the use of a unit or subassembly which generally comprises a molded centering piece of weldable plastic for connecting at least one branch pipe with a main pipeline, also formed of weldable plastic. The attachment unit or subassembly comprises a pair of arcuate parts which are to be placed around the main pipeline and which are to be welded thereto by means of an interposed electrical wire layer, with at least one of the parts of the attachment subassembly having a centering or branch piece.
One prior art embodiment of a molded centering piece of thermoplastic material is known from Swiss Pat. No. 528697 wherein a saddle part with a centering piece and a branch pipe embraces a main pipe together with a complimentary shell-shaped body secured by screws on the saddle part. In this embodiment, spirally wound bifiler or monofil sheathed welding wires are imbedded in an inner surface. In this molded centering piece, the saddle part and the shell-shaped body are individually welded and only locally welded with the main pipe. The assembly which must be performed on the construction site with screws necessary for the connection of the two parts is complicated and time consuming.
Furthermore, production of the two molded parts with the imbedded wire is elaborate, because of the relatively complicated arrangement of the welding wires.
It is an object of the present invention to provide a molded centering piece with a simple heating wire arrangement which is easy to produce and assemble, which can be arranged on a pipeline without additional screw joints with a minimum of assembly work, and which can be welded with the pipeline in an appropriate manner to insure a firm and tight branch connection.